Polyimide precursor, polyimide, and coating solution for under layer film for image formation

ABSTRACT

There is provided a polyimide precursor which can alter the hydrophilicity/hydrophobicity of the surface of a cured film formed readily even by a low level of ultraviolet ray irradiation; and a polyimide produced from the polyimide precursor. The polyimide precursor having a structure represented by the following formula (1): 
     
       
         
         
             
             
         
       
     
     (where A represents a tetravalent organic group; B represents a bivalent organic group having a thiol ester bond in its main chain; R 1  and R 2  independently represent a hydrogen atom or a univalent organic group; and n represents a natural number).

TECHNICAL FIELD

The present invention relates to a precursor of polyimide or a polyimidewhich is produced by dehydrating and ring closing this precursor ofpolyimide, and moreover, relates to electronic devices produced by usingthe precursor of polyimide or the polyimide.

BACKGROUND ART

A mask vapor deposition method or an etching method by photolithographyis mainly used for the pattern formation of electrodes or functionalthin films in the manufacturing process of electronic devices. Problemssuch as the difficulty of upsizing boards and complicated processes havebeen indicated in these related-art methods.

Recently, the application of a divisional coating technique utilizingwettability deference of liquids to the patterning of functional thinfilms has been developed instead of using these related-art methods.This divisional coating technique is a method for producing electronicdevices such as an organic electroluminescence (EL) element and anorganic field-effect transistor (FET) element by forming a patterninglayer including an easy-to-wet region and a difficult-to-wet region onthe surface of a substrate, and then applying and drying the solution ofa functional thin film forming material on this patterning layer to forma functional thin film only on the easy-to-wet region.

For such a patterning layer for a functional thin film, a layer made byirradiating a photocatalyst-containing layer made of titanium dioxideand organopolysiloxane with ultraviolet light through a mask (forexample, refer to Patent Document 1), a layer made by irradiating alayer made of a compound having light-absorbing parts, such as dyes, andfluorine-containing polymer with a laser or with ultraviolet lightthrough a mask (for example, refer to Patent Document 2) are known, forexample. In addition, also developed is a method of forming thepatterning layer by vapor deposition of a fluorine based coating agentthrough a mask (for example, refer to Patent Document 3).

Patterning layers developed to date, such as layers described in thePatent Documents, remain in the element even after the patterning offunctional thin films is completed. Therefore, this patterning layerneeds to have durability to subsequent processes and reliability of notproviding adverse effects to the properties of an electronic device whenthe patterning layer is in the electronic device. Such requiredproperties of the patterning layer vary depending on devicesmanufactured or the place to use the patterning layer. Among them, anelectrical insulation property is the important required property to thepatterning layer of an electrode.

Techniques developed to date have only focused on properties as apatterning layer. Therefore, for example, when a source electrode and adrain electrode of an organic FET element are patterned, a gateinsulating film needs to be separately prepared under the patterninglayer.

By contrast, polyimides have excellent heat resistance, mechanicalstrength, electrical insulation properties, chemical resistance and thelike. Therefore, polyimides are used for various electronic devices. Foran example of using a polyimide for a patterning layer, a layer using atetracarboxylic acid anhydride having an aliphatic ring structure (forexample, Patent Document 4) has been disclosed. However, long timeexposure treatment is necessary for these examples because thesematerials require extremely large amounts of ultraviolet rayirradiation.

Patent Document 1: Japanese Patent Application Publication No.JP-A-2000-223270

Patent Document 2: Japanese Patent Application Publication No.JP-A-2004-146478

Patent Document 3: Japanese Patent Application Publication No.JP-A-2004-273851

Patent Document 4: Japanese Patent Application Publication No.JP-A-2006-185898

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In order to solve the problems described above, it is an object of thepresent invention to provide a polyimide precursor which can alter thehydrophilicity/hydrophobicity of the surface of a cured film formedreadily even by a low level of ultraviolet ray irradiation; and apolyimide produced from the polyimide precursor.

Means for Solving the Problem

As a result of an intensive investigation for achieving theabove-described object, the present inventors have discovered that acontact angle to water is significantly altered with a small exposureamount when a polyimide precursor or a polyimide produced from thepolyimide precursor having a thiol ester structure in its main chain isused, and have accomplished the present invention.

Namely, according to a first aspect, the present invention relates to apolyimide precursor having a structure represented by the followingformula (1):

(where A represents a tetravalent organic group; B represents a bivalentorganic group having a thiol ester bond in its main chain; R¹ and R²independently represent a hydrogen atom or a univalent organic group;and n represents a natural number).

According to a second aspect, the present invention relates to thepolyimide precursor according to the first aspect, in which A in theformula (1) represents a tetravalent organic group having an aliphaticring or made of only an aliphatic group.

According to a third aspect, the present invention relates to thepolyimide precursor according to the first or the second aspect, inwhich B in the formula (1) represents a bivalent organic grouprepresented by the following formula (2):

(where X and Y independently represent an aromatic ring or an aliphaticring, and these rings may be substituted by a halogen atom or an alkylgroup having 1 to 4 carbon atom(s)).

According to a fourth aspect, the present invention relates to thepolyimide precursor according to any one of the first to the thirdaspects, in which the polyimide precursor is produced by polymerizing atleast one type of tetracarboxylic acid dianhydride represented by thefollowing formula (3) and a derivative thereof and at least one type ofa diamine represented by the following formula (4):

(where A represents a tetravalent organic group and B represents abivalent organic group having a thiol ester bond).

According to a fifth aspect, the present invention relates to apolyimide which is produced by dehydrating and ring closing thepolyimide precursor as described in any one of the first to the fourthaspects,

According to a sixth aspect, the present invention relates to a coatingsolution for an under layer film for image formation including at leastone type of a compound selected from a group consisting of the polyimideprecursor as described in any one of the first to the fourth aspects andthe polyimide as described in the fifth aspect.

According to a seventh aspect, the present invention relates to a curedfilm produced by curing the coating solution for an under layer film forimage formation as described in the sixth aspect.

According to an eighth aspect, the present invention relates to an underlayer film for image formation produced by using the coating solutionfor an under layer film for image formation as described in the sixthaspect.

According to a ninth aspect, the present invention relates to an underlayer film for electrode pattern formation produced by using the coatingsolution for an under layer film for image formation as described in thesixth aspect.

According to a tenth aspect, the present invention relates to a gateinsulating film produced by using the coating solution for an underlayer film for image formation as described in the sixth aspect.

According to an eleventh aspect, the present invention relates to amethod for forming an under layer film for image formation including:applying the coating solution for an under layer film for imageformation as described in the sixth aspect on a substrate, thermosettingit, and irradiating it with an ultraviolet ray.

EFFECTS OF THE INVENTION

A coating solution containing at least one type selected from a groupconsisting of a polyimide precursor and a polyimide produced from thepolyimide precursor according to the present invention can alter thesurface of a film formed from the solution from hydrophobicity tohydrophilicity by a low level of ultraviolet ray irradiation.Accordingly, an under layer film which is capable of image formation forfunctional materials such as electrodes or the like can be formed byutilizing these properties. A low level of ultraviolet ray irradiationcan alter the property of the surface of the film formed by the coatingsolution according to the present invention. As a result, this solutionis a highly valuable material with respect to productivity, becausesignificant reduction in process time in the manufacture of electronicdevices can be achieved.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention provides a polyimide precursor having a novelstructure, a polyimide produced from the polyimide precursor, and acoating solution for an under layer film for image formation containingat least one type of a compound selected from a group consisting of thepolyimide precursor and the polyimide. In addition, the presentinvention relates to a cured film produced from the coating solution andan electronic device using the cured film.

Details will be described below.

(Polyimide Precursor)

The present invention provides a polyimide precursor having a structurerepresented by the following formula (1):

(where A represents a tetravalent organic group; B represents a bivalentorganic group having a thiol ester bond; R¹ and R² independentlyrepresent a hydrogen atom or a univalent organic group; and n representsa natural number).

In the formula (1), the structure of an organic group represented by Ais not particularly limited, as long as the organic group is atetravalent organic group. In addition, the structure of the organicgroup represented by A in the polyimide precursor represented by theformula (1) may be one type or a combination of a plurality of types.Among them, A is preferably a tetravalent organic group having analiphatic ring or made of only an aliphatic group. More preferably, A isa tetravalent organic group having an aliphatic ring.

Preferable specific examples of the organic group represented by Ainclude organic groups of the following formulae A-1 to A-46.

TABLE 1 (Table 1 Formulae A-1 to A-24) A-1

A-2

A-3

A-4

A-5

A-6

A-7

A-8

A-9

A-10

A-11

A-12

A-13

A-14

A-15

A-16

A-17

A-18

A-19

A-20

A-21

A-22

A-23

A-24

TABLE 2 (Table 2 Formula A-25) A-25

TABLE 3 (Table 3 Formulae A-26 to A-36) A-26

A-27

A-28

A-29

A-30

A-31

A-32

A-33

A-34

A-35

A-36

TABLE 4 (Table 4 Formulae A-37 to A-46) A-37

A-38

A-39

A-40

A-41

A-42

A-43

A-44

A-45

A-46

The formulae A-1 to A-46 can be selected based on required propertieswhen an under layer film for image formation is made.

For example, in the formulae A-1 to A-46, tetravalent organic groupsthat improve exposure sensitivity (in the present specification,exposure sensitivity represents a conversion degree from hydrophobicityto hydrophilicity per an exposure amount (ultraviolet ray irradiationamount)) include tetravalent organic groups having an aliphatic ring offormulae A-1 to A-25 or made of only an aliphatic group. Particularly,A-1, A-6, A-16 or A-19 are exemplified as highly effective organicgroups.

In addition, tetravalent organic groups of formulae A-1 to A-25 ispreferable from the viewpoint of the effect of enhancing an insulationproperty.

In the formula (1), when organic groups other than the formulae A-1 toA-25 are mixed in the organic groups represented by A, a ratio of theformulae A-1 to A-25 is preferably 10 mol % or more, more preferably 50mol % or more, and most preferably 80 mol % or more.

In the formula (1), a bivalent organic group having a thiol ester bondrepresented by B is not particularly limited. However, preferableexamples of the bivalent organic group structure include a structure ofan aromatic ring such as a benzene ring bonded to the thiol ester group(the following formula (2)). It is considered that energy absorbed bythe aromatic ring is effectively transferred to the thiol ester group insuch a bivalent organic group. Consequently, it is presumed that thethiol ester group is decomposed, which leads to alter thehydrophilicity/hydrophobicity.

(where, X and Y independently represent an aromatic ring or an aliphaticring, and these rings may be substituted by a halogen atom or an alkylgroup having 1 to 4 carbon atoms).

Both of X and Y may be aromatic rings or one of them may be an aliphaticring in the formula (2). When one of X and Y is an aliphatic ring, theimprovement of insulation property can be expected.

Here, at least one of X or Y needs to be an aromatic ring forsufficiently absorbing an irradiated ultraviolet ray, when onlytetravalent organic groups having aliphatic rings are used as thetetravalent organic group represented by A from the viewpoint ofinsulation property.

The specific structures of the aromatic ring in X and Y are shown in thefollowing formulae (a) to (1). The formula (a) is particularlypreferable from the viewpoint of an insulation property.

In addition, the specific structures of aliphatic rings are shown in theformulae (m) to (s).

TABLE 5 (Table 5 X and Y: aromatic rings) (a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(l)

TABLE 6 (Table 6 X and Y: aliphatic rings) (m)

(n)

(o)

(p)

(q)

(r)

(s)

Preferable specific examples of the organic groups represented by Binclude organic groups of the following formulae B-1 to B-11.

TABLE 7 (Table 7 Formulae B-1 to B-11) B-1

B-2

B-3

B-4

B-5

B-6

B-7

B-8

B-9

B-10

B-11

In the under layer film for image formation produced from the polyimideprecursor or the polyimide of the present invention, the sensitivity ofthe under layer film to an ultraviolet ray is determined by theabsorbing wavelength of the polyimide precursor or the polyimide and bythe ease of decomposition by ultraviolet ray irradiation. Specifically,it is considered that the sensitivity increases in proportion to anamount of thiol ester groups (decomposition part) contained in theorganic group represented by B in the formula (1). Accordingly, whenfocusing particularly on the point that the formed under layer film forimage formation is highly sensitive, the most preferable ratio of thestructure derived from the polyimide precursor (and the polyimideproduced therefrom, as described below) represented by the formula (1)having a thiol ester bond in the under layer film for image formation is100 mol %.

The under layer film for image formation may have a structure derivedfrom the polyimide precursor (and the polyimide produced therefrom)represented by the following formula (5) in which the group B in theformula (1) is replaced with another bivalent organic group D having nothiol ester bond, in addition to the structure derived from thepolyimide precursor (and the polyimide produced therefrom) representedby the formula (1), when other properties, for example, the improvementof an insulation property, solubility in a solvent, as well ashydrophobicity of the film are considered as important properties.

In this case, the bond between the structure of the formula (1)containing the bivalent organic group B having a thiol ester bond andthe structure of the formula (5) containing another bivalent organicgroup having no thiol ester group may be any of a block bond and/or arandom bond.

(where, A, R¹, R² and n are the same definition as defined in theformula (1), and D represents another bivalent organic group having nothiol ester bond).

The ratio of the formula (1) containing the bivalent organic group Bhaving a thiol ester bond is preferably 30 mol % or more, because thesensitivity to an ultraviolet ray decreases when the content ratio ofthe formula (5) containing another bivalent organic group is too high.Moreover, the containing ratio of the formula (1) containing thebivalent organic group B having a thiol ester bond is required to befurther increased, and the ratio is preferably 50 mol % or more in orderto further increase the exposure sensitivity and reduce the irradiationtime of an ultraviolet ray.

Organic groups having a high insulation property are preferable for theother bivalent organic group D having no thiol ester bond in the formula(5). Specific examples of the organic group D include the organic groupsof the following formulae D-1 to D-57.

Among the following formulae D-1 to D57, the formulae D-1 to D-5 areexemplified in particular, as bivalent organic groups that are expectedto improve an insulation property.

In addition, examples of bivalent organic groups having a significanteffect of increasing solubility in a solvent include the formulae D-2,D-5, D-7, D-8, D-12, D-22, D-24 to D27, D-29 and the like.

Examples of bivalent organic groups that are expected to increasehydrophobicity of the surface of a cured film when the film is madeinclude the formulae D-43 to D-57. The formulae D-55 to D-57, in whichan alkyl group is added as a side chain, are exemplified as bivalentorganic groups that are particularly effective.

TABLE 8 (Table 8 Formulae D-1 to D-5) D-1

D-2

D-3

D-4

D-5

TABLE 9 (Table 9 Formulae D-6 to D-28) D-6

D-7

D-8

D-9

D-10

D-11

D-12

D-13

D-14

D-15

D-16

D-17

D-18

D-19

D-20

D-21

D-22

D-23

D-24

D-25

D-26

D-27

D-28

TABLE 10 (Table 10 Formulae D-29 to D-42) D-29

D-30

D-31

D-32

D-33

D-34

D-35

D-36

D-37

D-38

D-39

D-40

D-41

D-42

TABLE 11 (Table 11 Formulae D-43 to D-57) —(CH₂)_(n)— D-43 n = 2 ~ 12D-44

D-45

D-46

D-47

D-48

D-49

—(CH₂)₃—O—(CH₂)₂—(CH₂)₃— D-50 D-51

D-52

D-53

D-54

D-55

D-56

D-57

In the formula (1), each of R¹ and R² is a hydrogen atom or a univalentorganic group. Examples of R¹ and R² include alkyl groups having 1 to 4carbon atom(s).

Examples of the alkyl groups having 1 to 4 carbon atom(s) include amethyl group, ethyl group, propyl group, isopropyl group, butyl group,isobutyl group and t-butyl group.

The polyimide precursor according to the present invention is notparticularly limited, as long as the precursor has each organic groupdescribed above. However, polyimide precursors (polyamic acids)represented by the following formula (6) is preferable because thepolyimide precursor is relatively readily produced when atetracarboxylic acid anhydride and a diamine are used as startingmaterials.

(where, A, B, R¹, R² and n are the same definition as defined in theformula (1)).

(Method for Manufacturing Polyimide Precursor)

The polyimide precursor according to the present invention ismanufactured by polymerizing a tetracarboxylic acid dianhydride andderivatives thereof and dianime.

(Tetracarboxylic Acid Dianhydride and Derivatives Thereof)

Tetracarboxylic acid dianhydride and derivatives thereof are representedby a structure of the general formula (3) shown below, and A representsa tetravalent organic group. Specific examples of the tetravalentorganic group include the formulae A-1 to A-46.

(where A is a tetravalent organic group, and B represents a bivalentorganic group having a thiol ester bond in its main chain).

As described above, A is preferably the organic group having a largenumber of tetravalent organic groups containing an aliphatic ring, thatis, a compound represented by the formula (3) having a higher ratio ofan aliphatic acid anhydride.

This is because, an aliphatic acid anhydride has an excellent insulationproperty at high electrical field, although insulation property isremarkably decreased by applying high electrical field to a cured filmwhen the polyimide precursor or the like is manufactured by using anaromatic acid anhydride and the cured film is produced from thispolyimide precursor.

For example, since an operating voltage of an organic transistor may beabout 1 MV/cm, an aliphatic acid anhydride is desirably used as astarting material for the polyimide precursor from the viewpoint ofinsulation property, when the polyimide precursor is used for thisapplication.

(Diamine)

Diamine is represented by a structure of the general formula (4) shownbelow. B is a bivalent organic group having a thiol ester bond in itsmain chain, and specific examples of B include the organic groups shownin the above formulae B-1 to B-11.

[Chemical Formula 9]

H₂N—B—NH₂  (4)

In addition, diamines other than the diamine represented by the formula(4) can be used within the range which achieves the effect of thepresent invention. Specific examples of the diamine include diamineshaving a bivalent organic group represented by the formulae C-1 to C-57.

(Method for Manufacturing Polyimide Precursor)

A method of mixing a tetracarboxylic acid dianhydride componentrepresented by the formula (3) and a diamine component represented bythe formula (4) in an organic solvent is convenient for producing thepolyimide precursor having repeating units represented by the formula(1).

Examples of the method of mixing a tetracarboxylic acid dianhydridecomponent and a diamine component in an organic solvent include: amethod of stirring a solution in which the diamine component isdispersed or dissolved in the organic solvent, and adding thetetracarboxylic acid dianhydride component as it is, or dispersed ordissolved in the organic solvent; or, in contrast, a method of addingthe diamine component to a solution in which the tetracarboxylic aciddianhydride component is dispersed or dissolved in the organic solvent;or a method of alternately adding the tetracarboxylic acid dianhydridecomponent and the diamine component.

Moreover, when compounds having a plurality of types of tetracarboxylicacid dianhydride components and diamine components are used, theplurality of types of components may be mixed and then polymerized, ormay be individually polymerized in sequence.

When the polyimide precursor used in the present invention ismanufactured from the tetracarboxylic acid dianhydride componentrepresented by the formula (3) and the diamine represented by theformula (4), the blended ratio of both components, that is, (totalnumber of moles of tetracarboxylic acid dianhydride component):(totalnumber of moles of diamine component) is desirably from 1:0.5 to 1:1.5.As the molar ratio approaches 1:1, the degree of polymerization of thepolyimide precursor produced increases, whereby the molecular weightincreases, similarly to general polycondensation reactions.

In the method of manufacturing the polyimide precursor, a temperature atwhich the reaction of the tetracarboxylic acid dianhydride component andthe diamine component in an organic solvent is effected is generally −20to 150° C., preferably from 0 to 80° C.

The polymerization reaction rapidly proceeds to be completed, when thereaction temperature is set to high. However, the polyimide precursorhaving a high molecular weight may not be produced, when the reactiontemperature is too high.

The solid content concentration of both components (the tetracarboxylicacid anhydride component and the diamine component) in a solvent is notparticularly limited for the polymerization reaction in the organicsolvent. However, when the concentration is too low, it is difficult toproduce the polyimide precursor having a high molecular weight, and whenthe concentration is too high, homogeneous stirring becomes difficultbecause the viscosity of the reaction solution is too high. Therefore,preferable concentration is 1 to 50% by mass, and more preferably from 5to 30% by mass. It is also possible that polymerization at an initialstage is performed at high concentration, and then the polymer (thepolyimide precursor) is purified and then an organic solvent is added.

The organic solvent used in the polymerization reaction is notparticularly limited, as long as the produced polyimide precursor isdissolved therein. However, specific examples of the organic solventinclude dimethylformamide, N,N-dimethylformacetamide,N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethylsulfoxide,tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide, andγ-butyrolactone. These solvents can be used singly or in combination oftwo or more thereof. Moreover, a solvent which dissolves no polyimideprecursor may be added to the solvent within the range in which theproduced polyimide precursor is not deposited.

The solution containing thus produced polyimide precursor can be usedwithout modification to prepare a coating solution for an under layerfilm for image formation described below. In addition, the polyimideprecursor can also be recovered and used by precipitating the polyimideprecursor in a poor solvent such as water, methanol, or ethanol andisolating the precipitate.

(Polyimide)

The polyimide precursor having repeating units represented by theformulae (1) and (6) (and the formula (5)) can transform into apolyimide by dehydration and ring closure. A method for this imidizationreaction is not particularly limited. However, catalyst imidizationusing a basic catalyst and an acid anhydride is preferable because thedecrease in molecular weight in polyimide during the imidizationreaction does not easily occur and the control of an imidization ratiois easy.

The catalyst imidization can be performed by stirring the polyimideprecursor in the organic solution in the presence of a basic catalystand an acid anhydride for 1 to 100 hour(s).

Here, the solution containing the polyimide precursor produced from thepolymerization of the tetracarboxylic acid anhydride component anddiamine component may be used without modification (without isolation).

Examples of the basic catalyst can include pyridine, triethylamine,trimethylamine, tributylamine, and trioctylamine. Among them, pyridineis preferable because pyridine has moderate basicity for the progress ofthe reaction.

Examples of the acid anhydride can include acetic acid anhydride,trimellitic acid anhydride, and pyromellitic acid anhydride. Among them,acetic acid anhydride is preferable because the produced polyimide isreadily purified after the completion of imidization.

The solvent used in the polymerization reaction of the polyimideprecursor can be used for the organic solvent.

The reaction temperature for the catalyst imidization is preferably from−20 to 250° C., and more preferably from 0 to 180° C. The imidizationproceeds rapidly when a reaction temperature is set to high. However,the molecular weight of the polyimide may decrease, when the reactiontemperature is too high.

The amount of the basic catalyst with respect to acid amide group in thepolyimide precursor is preferably from 0.5 to 30 times by mole, and morepreferably from 2 to 20 times by mole. Moreover, the amount of the acidanhydride with respect to acid amide group in the polyimide precursor ispreferably from 1 to 50 times by mole, and more preferably from 3 to 30times by mole.

The imidization ratio of the polyimide produced can be controlled byadjusting the reaction temperature and the amount of catalyst.

The reaction solution of the solvent soluble polyimide produced asdescribed above can be used for producing a gate insulating filmdescribed below without modification. However, the polyimide afterpurification/recovery/washing is preferably used for film production,since the imidization catalyst and the like are contained in thereaction solution.

A method of precipitating the polyimide by feeding the reaction solutioninto a poor solvent with stirring and filtering the precipitate isconvenient for the recovery of polyimide.

The poor solvent used for this process is not particularly limited.However, methanol, hexane, heptane, ethanol, toluene, water and the likecan be exemplified. Washing is preferably performed using the poorsolvent, after recovering the precipitate by filtration.

Polyimide powder can be made from the recovered polyimide by drying atambient temperature or by heating under normal pressure or reducedpressure.

Impurity in the polymer can be further reduced by repeating theoperation, in which this polymer powder is dissolved into a good solventand the polyimide is reprecipitated by the poor solvent, for 2 to 10times.

The good solvent used in this operation is not particularly limited, aslong as the polyimide precursor or the polyimide can be dissolved.Examples of the good solvents include N,N-dimethylformamide,N,N-dimethylacetamide, 2-pyrrolidone, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-methylcaprolactam,dimethylsulfoxide, tetramethylurea, pyridine, and γ-butyrolactone.

In addition, the efficiency of purification is further improved when atleast three types of poor solvents such as alcohols, ketones, andhydrocarbons are used for reprecipitation.

(Coating Solution for Under Layer Film for Image Formation)

A coating solution for an under layer film for image formation accordingto the present invention is a coating solution which contains thepolyimide precursor and the polyimide according to the present inventionas well as the solvent, and can further contain a coupling agent, asurfactant and the like described below, if desired.

The molecular weight of the polyimide precursor and/or the polyimideused for the coating solution for an under layer film for imageformation according to the present invention is preferably a polystyreneconversion weight average molecular weight of 2,000 to 200,000(measurement results measured by GPC), and more preferably 5,000 to50,000, from the viewpoint of easy handling and stability of solventresistance in film formation or the like.

The altering amount of hydrophilicity/hydrophobicity is notsignificantly different between the polyimide precursor and thepolyimide, when a cured film is produced by using the coating solutionfor an under layer film for image formation according to the presentinvention and an ultraviolet ray is used to irradiate the film.Therefore, an imidization ratio is not particularly limited, when thecured film produced places emphasis on this point.

However, the polyimide is preferably used, because, by using thepolyimide, a highly reliable film having low baking temperature (180° C.or less), at which a plastic substrate is usable, can be produced, and ahigh contact angle to water (high hydrophobicity) prior to ultravioletray irradiation can be obtained because polyimide has low polaritycompared with the polyimide precursor.

On the contrary, the imidization ratio of the coating solution ispreferably 90% or more, when the coating solution for an under layerfilm for image formation according to the present invention is used fora cured film (for example, a gate insulating film) which places emphasison an insulation property. However, the imidization ratio can be reducedwhen solubility in a solvent is impaired. In this case, a highinsulation property as an under layer film can be maintained by highimidization (high insulation property) of the lowermost layer using ablend technique as described below when the film is formed. Thus, thetechnique is useful.

The solvent used for the coating solution for an under layer film forimage formation according to the present invention is not particularlylimited, as long as the solvent can dissolve the polyimide precursor orthe polyimide. Examples of the solvent include good solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, 2-pyrrolidone,N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone,N-methylcaprolactam, dimethylsulfoxide, tetramethylurea, pyridine, andγ-butyrolactone. These solvents may be used singly or in combination. Inaddition, poor solvents such as alcohols, ketones, and hydrocarbons maybe used by mixing with the good solvents.

The ratio of solid content in the coating solution for an under layerfilm for image formation according to the present invention is notparticularly limited, as long as each component, including a couplingagent and the like as described below, is homogeneously dissolved in thesolvent. However, for example, the ratio of solid content is 1 to 30% bymass or, for example, 5 to 20% by mass. Here, the solid content meansthe remains after the solvent is removed from the total components ofthe coating solution for an under layer film for image formation.

The method for preparing the coating solution for an under layer filmfor image formation according to the present invention is notparticularly limited. However, a solution containing the polyimideprecursor produced by polymerization of the tetracarboxylic acidanhydride component and diamine component or a reaction solution ofpolyimide produced by using the solution may be used withoutmodification.

In addition, a coupling agent can be further included in the coatingsolution for an under layer film for image formation of the presentinvention in order to increase adhesion between the coating solution anda substrate, unless the coupling agent impairs the effect of the presentinvention.

Examples of the coupling agent include functional silane compounds andepoxy-containing compounds. Specific examples of the coupling agents caninclude compounds such as 3-aminopropyltrimethoxysilane,3-aminopropyltriethoxysilane, 2-aminopropyltrimethoxysilane,2-aminopropyltriethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,3-ureidepropyltrimethoxysilane, 3-ureidepropyltriethoxysilane,N-ethoxycarbonyl-3-aminopropyltrimethoxysilane,N-ethoxycarbonyl-3-aminopropyltriethoxysilane,N-trimethoxysilylpropyltriethylenetriamine,N-triethoxysilylpropyltriethylenetriamine,10-trimethoxysilyl-1,4,7-triazadecane,10-triethoxysilyl-1,4,7-triazadecane, 9-trimethoxysilyl-3,6-diazanonylacetate, 9-trieethoxysilyl-3,6-diazanonyl acetate,N-benzyl-3-aminopropyltrimethoxysilane,N-benzyl-3-aminopropyltriethoxysilane,N-phenyl-3-aminopropyltrimethoxysilane,N-phenyl-3-aminopropyltriethoxysilane,N-bis(oxyethylene)-3-aminopropyltrimethoxysilane,N-bis(oxyethylene)-3-aminopropyltriethoxysilane, ethylene glycoldiglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycoldiglycidyl ether, tripropylene glycol diglycidyl ether, polypropyleneglycol diglycidyl ether, neopentyl glycol diglycidyl ether,1,6-hexanediol diglycidyl ether, glycerin diglycidyl ether,2,2-dibromoneopentyl glycol diglycidyl ether,6-tetradiglycidyl-2,4-hexanediol,N,N,N′,N′-tetraglycidyl-m-xylenediamine,1,3-bis(N,N-diglycidylaminomethyl)cycIohexane andN,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane.

These coupling agents may be used singly or in combination of two ormore thereof.

When the coupling agent is used, its content is preferably from 0.1 to30 parts by mass, and more preferably from 1 to 20 part(s) by mass basedon 100 parts by mass of the coating solution for an under layer film forimage formation.

Moreover, the coating solution for an under layer film for imageformation of the present invention can contain a surfactant in order toimprove coatability of the coating solution, and uniformity of filmthickness and surface smoothness of the film produced from the coatingsolution.

The surfactant is not particularly limited. However, for example,fluorine-based surfactants, silicone-based surfactants, and nonion-basedsurfactants are included. Examples of these types of surfactants includeEftop EF301, EF303, EF352 (manufactured by JEMCO, Inc.), Megafac F171,F173, R-30 (manufactured by DIC Corporation), Fluorad FC430, FC431(manufactured by Sumitomo 3M Limited), AsahiGuard AG710 and SurflonS-382, SC101, SC102, SC103, SC104, SC105, SC106 (manufactured by AsahiGlass Co., Ltd.).

When the surfactant is used, its content is preferably from 0.01 to 2parts by mass, and more preferably from 0.01 to 1 part(s) by mass basedon 100 parts by mass of the polymer component contained in the coatingsolution for an under layer film for image formation.

(Regarding Polymer Blend)

The coating solution for an under layer film for image formationaccording to the present invention can also take a form of what iscalled a polymer blend by mixing other polymers which can form a film(for example, a high insulation polymer) in addition to the polyimideprecursor or the polyimide of the present invention.

In the polymer blend, by properly controlling the structure of containedpolymers (the polyimide precursor and the polyimide according to thepresent invention and other polymers), the concentration gradient ofeach polymer in the thickness direction in the film can be generatedwhen the cured film is formed. Thus, the technique can be used as auseful procedure.

For example, alteration of hydrophilicity/hydrophobicity has aninfluence only on the surface of the film. From the viewpoint of this,the polyimide precursor and/or the polyimide according to the presentinvention having thiol ester bonds may only exist in the upper layer(the surface layer) of the cured film.

Accordingly, when the coating solution for an under layer film for imageformation is in the form of polymer blend (hereinafter, the coatingsolution in this form is referred to as a blended coating solution), theblended ratio of the polyimide precursor or the polyimide according tothe present invention is 1% by mass to 100% by mass to the total mass ofthe blended coating solution. When the blended ratio is 1% by mass orless, image forming ability may deteriorate when the film is formed fromthe blended coating solution because it is difficult to completely coverthe top surface of the film.

The polymer blend can be useful, for example, in the case of using thecoating solution for an under layer film for image formation accordingto the present invention for the application of gate insulating film forwhich a high insulation property is particularly required.

Various properties such as applicability to a baking temperature of 180°C. or below, capability of film formation by application, solventresistance to an organic semiconductor coating solution (non-polarsolvents such as xylene and trimethyl benzene) and low moistureabsorbance are required for the coating solution, when the solution isused for the application of a gate insulating film. Particularly, aninsulation property is highly required. An imidization ratio for thecoating solution for an under layer film for image formation accordingto the present invention may be required at least 80% or more, and 90%or more in some cases for achieving this high insulation property. Onthe contrary, solubility in a solvent is lost, when the imidizationratio exceeds 90%. in this case, by disposing the high insulation layeronly as the lowermost layer of the insulation film and disposing a layermade from the coating solution for an under layer film for imageformation according to the present invention as the upper layer, thehigh insulation property of the insulation film is retained and theproblem of solubility is also resolved.

As described above, the high insulation layer as the lower layer of thecured film and the hydrophilicity/hydrophobicity altering layer as theupper layer can be produced by laminating these layers in order.However, this operation is cumbersome.

At this time, when the material for the high insulation layer and thematerial for the hydrophilicity/hydrophobicity altering layer (that is,the polyimide precursor and/or the polyimide according to the presentinvention) is mixed and the polarity or the molecular weight of thematerial for the upper layer is made to be low compared with thematerial for the lower layer, the above-described concentration gradient(means phase separation) can be readily controlled, because a materialfor the upper layer shows a behavior of migrating to the surface to forma layer during the evaporation of a solvent after the mixed solution isapplied to the substrate and dried.

A soluble polyimide is the most preferable forming material for the highinsulation film which can form the lower layer. When the solublepolyimide is used for the material for lower layer, the imidizationratio of the polyimide in the solution is desired to be high and is atleast 50% or more, preferably 80% or more, and most preferably 90% ormore from the viewpoint of insulation property.

Examples of other materials capable of being used for the lower layermaterial include general organic polymers such as epoxy resins, acrylresins, polypropylene, polyvinyl alcohol, polyvinyl phenol,polyisobutylene and polymethylmethacrylate.

The content ratio of the polyimide precursor and/or the polyimideaccording to the present invention in the polymer blend required to formthe upper layer (the hydrophilicity/hydrophobicity altering layer) istheoretically about 1%, when the above-described polymer blend is usedfor, for example, an application of an organic transistor whose requiredfilm thickness is around 400 nm. However, the content of the polyimideprecursor and/or the polyimide is preferably at least 5% or more,because excessively low content results in large variation of physicalproperties in the surface of the cured film.

(Method for Manufacturing Coating Film and Cured Film)

The coating solution for an under layer film for image formation of thepresent invention is applied to a glass substrate or a plastic substratemade of general-purpose polymers such as polypropylene, polyethylene,polycarbonate, polyethylene terephtalate, polyethersulfone, polyethylenenaphtalate and polyimide by a dipping method, a spin-coating method, atransferring printing method, a roll coating method, an ink jet method,a spray method, a brush coating and the like. Then, the coating film canbe formed by pre-drying by using a hot plate or an oven. Subsequently, acured film capable of using as an under layer film for image formationor an insulation film is formed by subjecting this coating film to heattreatment.

The method of the heat treatment is not particularly limited. However, amethod of heating under an appropriate atmosphere, that is, air, inertgas such as nitrogen, or under vacuum, using a hot plate or an oven canbe exemplified.

The baking temperature is preferably from 180° C. to 250° C. from theviewpoint of accelerating thermal imidization of the polyimideprecursor, and is preferably 180° C. or less from the viewpoint of thefilm formation on a plastic substrate.

The baking temperature may vary in more than two stages. The uniformityof the produced film can be further improved by stepwise baking.

Moreover, the coating solution for an under layer film for imageformation can be used for applying onto a substrate without modificationfor forming the cured film because the coating solution is in the formof including the polyimide precursor and/or the polyimide and theabove-described solvents. However, this solution may further include thesolvents and other various solvents, and may be used as a coatingsolution in order to control the concentration, to ensure the coatingfilm flatness, to improve the wettability of the coating solution to asubstrate, to adjust the surface tension, polarity and boiling point ofthe coating solution, and so on.

Specific examples of such solvents include: ethyl cellosolve, butylcellosolve, ethyl carbitol, butyl carbitol, ethyl carbitol acetate,ethylene glycol and the like; propylene glycol derivatives such as1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol,1-phenoxy-2-propanol, propylene glycol monoacetate, propylene glycoldiacetate, propylene glycol-1-monomethyl ether-2-acetate, propyleneglycol-1-monoethyl ether-2-acetate, dipropylene glycol,2-(2-methoxypropoxy)propanol, 2-(2-ethoxypropoxy)propanol and2-(2-butoxypropoxy)propanol; lactic acid derivatives such as methyllactate, ethyl lactate, n-propyl lactate, n-butyl lactate, and isoamyllactat, in addition to the solvents described in the paragraph [0074].These solvents may be used singly or in combination of two or morethereof.

From the viewpoint of the improvement of storage stability of thecoating solution and thickness uniformity of the coating film, 20 to 80%by mass to the mass of the entire solvent is preferably at least onesolvent selected from N,N-dimethylformamide, N,N-dimethylacetamide,N-methyl-2-pyrrolidone, γ-butyrolactone and dimethylsulfoxide.

The concentration of the coating solution is not particularly limited.However, the solid content concentration of the polyimide precursor andthe polyimide is preferably from 0.1 to 30% by mass, and more preferablyfrom l to 10% by mass. This concentration is appropriately determineddepending on specifications of coating equipment and a desired filmthickness.

When the cured film of the present invention produced as described aboveis used for an under layer film for image formation, if the filmthickness is too thin, patternability after ultraviolet ray irradiationis degraded, and if too thick, the uniformity of the surface isimpaired. Accordingly, the film thickness is preferably from 5 nm to1000 nm, more preferably from 10 nm to 300 nm, and most preferably from20 nm to 100 nm.

In addition, the cured film according to the present invention alsofunctions as an insulation film when its insulation property issufficiently high. In this case, the cured film is used as a gateinsulating film directly disposed on a gate electrode, for example, ofan organic FET device. On this occasion, the film thickness of the curedfilm is desirably thicker than that of the under layer film for imageformation in order to ensure the insulation property. The film thicknessis preferably from 20 nm to 1000 nm, more preferably from 50 nm to 800nm, and most preferably from 100 nm to 500 nm.

[Method for Manufacturing Electrode for Image Formation]

An electrode for image formation can be manufactured by irradiating theunder layer film for image formation according to the present inventionwith an ultraviolet ray in a patterned shape, and then applying an imageformation solution as described below.

In the present invention, the method for irradiating the under layerfilm for image formation with an ultraviolet ray in a patterned shape isnot particularly limited. However, for example, a method of irradiationthrough a mask in which an electrode pattern is drawn, a method ofdrawing an electrode pattern by using a laser beam and other methods canbe included.

The material and shape of the mask is not particularly limited. Thismask may be transparent to an ultraviolet ray in the region required foran electrode, and opaque to an ultraviolet ray in other region.

At this time, an ultraviolet ray having a wavelength in the range from200 nm to 500 nm can be generally used. An appropriate wavelength isdesirably selected through a filter and the like depending on the typesof polyimide used. Specifically, the wavelengths of 248 nm, 254 nm, 303nm, 313 nm, 365 nm and the like are included. Particularly, thewavelengths of 248 nm and 254 nm are preferred.

The surface energy of the under layer film for image formation accordingto the present invention gradually increases by ultraviolet rayirradiation and is saturated with the sufficient amount of irradiation.This increase of the surface energy brings a decrease of the contactangle of an image formation solution. As a result, the wettability ofthe image formation solution increases at a part that is irradiated withultraviolet ray.

Accordingly, when the image formation solution is applied to the underlayer film for image formation according to the present invention afterultraviolet ray irradiation, an electrode having any patterned shape canbe produced as follows: the image formation solution forms a pattern inself-organization along a patterned shape drawn on the under layer filmfor image formation as difference of the surface energy.

Consequently, the required amount of ultraviolet ray irradiation to theunder layer film for image formation is an irradiation amount whichsufficiently alters the contact angle of the image formation solution.The irradiation amount is preferably 40 J/cm² or less, more preferably30 J/cm² or less and most preferably 20 J/cm² or less from the viewpointof energy efficiency and shortening the manufacturing process time.

In addition, the larger the difference of the contact angle of the imageformation solution between the ultraviolet ray irradiation part and theultraviolet ray non-irradiation part of the under layer film for imageformation, the easier the patterning. Therefore, the electrode can beproduced into complicated patterns and microscopic patterned shapes.Accordingly, the altered amount of the contact angle by ultraviolet rayirradiation is preferably 10° or more, more preferably 30° or more, andmost preferably 50° or more.

Based on a similar reason, the contact angle of the image formationsolution is preferably 50° or more at the ultraviolet raynon-irradiation part and 30° or less at the ultraviolet ray irradiationpart.

At the present day, water is often used for the solvent of the imageformation solution. Therefore, the performance evaluation of the underlayer film can be performed by replacing the altered amount of thecontact angle of the image formation solution with the altered amount ofthe contact angle of water in order to simplify the measurement.

The image formation solution according to the present invention is acoating solution which can be used as a functional film made by applyingthe solution to the substrate, and then evaporating the solventcontained in the image formation solution. For example, a solution inwhich a charge transport material is dissolved or homogeneouslydispersed in at least one type of solvents is included. Here, a chargetransport property has the same definition as conductivity, and meansany one of a hole transport property, an electron transport property,and a charge transport property of both of holes and electrons.

The charge transport material is not particularly limited, as long as ithas conductivity capable of transporting holes or electrons. Examples ofthe charge transport material include metal fine particles of gold,silver, copper, aluminum, and the like; inorganic materials such ascarbon blacks, fullerenes and carbon nano tubes; and organicπ-conjugated polymers such as polythiophene, polyaniline, polypyrrole,polyfluorene and derivatives thereof.

In addition, charge receiving materials such as halogens, Lewis acids,protonic acids and transition metal compounds (specific examplesincluding Br₂, I₂, Cl₂, FeCl₃, MoCl₅, BF₃, AsF₅, SO₃, HNO₃, H₂SO₄, andpolystyrene sulfonic acid) or charge donating materials such as alkalimetals and alkyl ammonium ions (specific examples including Li, Na, K,Cs, tetraethylene ammonium, and tetrabutyl ammonium) may further beadded to the image formation solution as dopants in order to improve thecharge transport property of the charge transport material.

The solvent for the image formation solution is not particularlylimited, as long as the charge transport material or the dopants can bedissolved or homogeneously dispersed in the solvent. However, water andvarious alcohols are preferable from the viewpoint of producing preciseelectrode pattern, since it is preferable that a sufficiently largecontact angle is provided to the ultraviolet ray non-irradiation part ofthe under layer film for image formation and less damage is given to theunder layer film for image formation according to the present invention.

In addition, polar solvents such as N,N-dimethylformamide,N,N-dimethylacetamide, 2-pyrrolidone, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-methylcaprolactam,dimethylsulfoxide and tetramethylurea are also preferable from theviewpoint of having excellent solubility of the organic based chargetransporting material, and providing a sufficiently large contact angleto the ultraviolet ray non-irradiation part of the under layer film forimage formation of the present invention. However, these solvents arepreferably used in a range in which the under layer film for imageformation according to the present invention is less damaged.

The concentration of the charge transporting material in the imageformation solution is preferably from 0.01 to 30% by mass, morepreferably from 0.1 to 10% by mass, and most preferably from 1 to 5% bymass.

Specific examples of the image formation solution according to thepresent invention include Baytron (registered trademark) P(polyethylenedioxythiophene, manufactured by Bayer AG).

An electrode according to the present invention is produced by applyingthe image formation solution on the under layer film for image formationaccording to the present invention and evaporating the solvent afterpattern formation. The method of evaporating the solvent is notparticularly limited. However, evaporating the solvent under anappropriate atmosphere, that is, air, inert gas such as nitrogen, orunder vacuum using a hot plate or an oven, can produce the uniformsurface of the formed film.

The temperature for evaporating the solvent is not particularly limited.However, evaporation is preferably performed at 40 to 250° C. Theevaporation temperature may vary in more than two stages from theviewpoint of achieving the retention of patterned shape and theuniformity of film thickness.

The electrode made from this image formation solution is used forelectrodes of electronic devices such as field-effect transistors,bipolar transistors, various diodes and various sensors, as well aswirings for connecting electronic devices.

The electronic device according to the present invention has theelectrode according to the present invention.

An example of the under layer film for image formation of the presentinvention used for an organic FET element will be described. However,the present invention is not limited to this example.

First, a high doping n-type silicon substrate is prepared. It ispreferable that the substrate is cleaned in advance by liquid washingwith a detergent, an alcohol, purified water or the like, and surfacetreatment such as ozone treatment and oxygen-plasma treatment ispreferably performed just before its use. A film of SiO₂, Ta₂O₅, Al₂O₃or the like is formed on a substrate by methods such as thermaloxidation, sputtering, CVD or vapor deposition to form a gate insulatingfilm. The film thickness of the gate insulation layer is preferably from30 nm to 1000 nm based on the relationship between drive voltage andelectrical insulation property, although it depends on the applicationsof the organic FET.

Next, a layer containing the polyimide precursor and/or the polyimidehaving repeating units represented by the formula (1) is formed inaccordance with the above-descried procedures on the insulating film.The film thickness of the layer is most preferably from 20 nm to 100 nm.Subsequently, an ultraviolet ray is radiated in a patterned shapethrough a mask or the like.

Subsequently, an image formation solution using a polar solvent such aswater is applied to the surface of the under layer film for imageformation. The applied image formation solution rapidly spreads to ahydrophilic part (an ultraviolet ray irradiation part) while beingrepelled by a hydrophobic part (an ultraviolet ray non-irradiationpart), and is then stabilized. By drying the stabilized solution, apatterned source and drain electrodes are formed. The coating method forthe image formation solution is not particularly limited. However, anink jet printing method or spray coating method is preferable due to theease of liquid volume control.

Finally, the formation of the organic FET is completed by forming a filmof an organic semiconductor material such as pentacene and polytiophene,which is an active layer of the organic FET. The method of filmformation of the organic semiconductor material is not particularlylimited. However, vacuum deposition, as well as a spin-coating method, acasting method, an inkjet method, a spray method and other methods usingthe solution may be included.

The organic FET manufactured as described above can remarkably reducethe manufacturing processes. Moreover, large current can be extracted inthe case of using an organic semiconductor material having low mobilityas an active layer, because an organic FET having a shorter channel thanthe channel made by mask vapor deposition method can be manufactured. Inaddition, the under layer film for image formation produced by themethod according to the present invention can also be used as a gateinsulation layer, because the film has an excellent electric insulationproperty. Thus, the manufacturing process can further be simplified.

EXAMPLES

The present invention will be described further in detail hereinafterwith reference to examples. However, the present invention is notlimited to these examples.

(Measurement of Number Average Molecular Weight and Weight AverageMolecular Weight)

The number average molecular weight (hereinafter referred to as Mn) andthe weight average molecular weight (hereinafter referred to as Mw) ofthe polyimide precursors produced according to the following SynthesisExamples are measured by GPC (ambient temperature gel permeationchromatography) with the following equipment and measurement conditions,and calculated as polyethylene glycol (or polyethylene oxide) conversionvalue.

GPC equipment: Shodex (registered trademark) (GPC-101), manufactured byShowa Denko K.K

Column: Shodex (registered trademark) (serial connection of KD803 andKD805), manufactured by Shown Denko K.K

Column temperature: 50° C.

Eluent: N,N-dimethylformamide

(lithium bromide hydrate (LiBr.H₂O) 30 mmol/L, phosphoric acid anhydrouscrystal (o-phosphoric acid) 30 mmol/L and tetrahydrofuran (THF) 10 ml/L,as additives)

Flow rate: 1.0 ml/min

Standard sample for preparing calibration curve:

TSK standard polyethylene oxide (molecular weight: about 900,000,150,000, 100,000 and 30,000), manufactured by Tosoh Corporation

Polyethylene glycol (molecular weight: about 12,000, 4,000 and 1,000),manufactured by Polymer Laboratories Ltd.

(Measurement of Film Thickness)

The film thickness of a polyimide film was determined by measuring alevel difference prepared by peeling a part of the polyimide films usinga retractable knife, using a fully automatic microfigure measuringinstrument (ET4000A, manufactured by Kosaka Laboratory Ltd.) at ameasuring force of 10 μN and a sweeping speed of 0.05 mm/sec.

Synthesis Example 1 Polymerization of Polyimide Precursor (PI-1)

Under nitrogen stream, 2.4431 g (0.01 mol) of 4-amino-S-thiobenzoicacid-4′-aminophenyl (hereinafter referred to as DA-25) was fed into a 50ml four-neck flask and dissolved into 24.62 g of N-methyl-2-pyrrolidone(hereinafter, NMP). Subsequently, 1.955 g (0.01 mol) of1,2,3,4-cyclobutanetetracarboxylic acid anhydride (hereinafter, CBDA)was added and the mixture was stirred for 10 hours at 23° C. to performa polymerization reaction. Furthermore, this mixture was diluted withNMP to obtain 6% by weight solution of the polyimide precursor (PI-1).

The number average molecular weight (Mn) and weight average molecularweight (Mw) of the produced polyimide precursor (PI-1) were Mn=17,700and Mw=38,300, respectively.

Synthesis Example 2 Polymerization of Polyimide Precursor (PI-2)

Under nitrogen stream, 1.466 g (0.006 mol) of DA-25 was fed into a 50 mlfour-neck flask and dissolved into 18.313 g of NMP. Subsequently, 1.772g (0.006 mol) of 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinicacid anhydride (hereinafter, TDA) was added and the mixture was stirredfor 24 hours at 50° C. to perform a polymerization reaction.Furthermore, this mixture was diluted with NMP to obtain 6% by weightsolution of the polyimide precursor (PI-2).

The number average molecular weight (Mn) and weight average molecularweight (Mw) of the produced polyimide precursor (PI-2) were Mn=5,200 andMw=7,900, respectively.

Synthesis Example 3 Polymerization of Polyimide Precursor (PI-3)

Under nitrogen stream, 1.466 g (0.006 mol) of DA-25 was fed into a 50 mlfour-neck flask and dissolved into 16.644 g of NMP. Subsequently, 1.486g (0.006 mol) of bicyclo(3,3,0)-octane-2,4,6,8-tetracarboxylic acidanhydride (hereinafter, BODA) was added and the mixture was stirred for24 hours at 80° C. to perform a polymerization reaction. Furthermore,this mixture was diluted with NMP to obtain 6% by weight solution of thepolyimide precursor (PI-3).

The number average molecular weight (Mn) and weight average molecularweight (Mw) of the produced polyimide precursor (PI-3) were Mn=4,900 andMw=7,200, respectively.

Synthesis Example 4 Polymerization of Polyimide Precursor (PI-4)

Under nitrogen stream, 1.466 g (0.006 mol) of DA-25 was fed into a 50 mlfour-neck flask and dissolved into 15.50 g of NMP. Subsequently, 1.269 g(0.006 mol) of pyromellitic acid dianhydride (hereinafter, PMDA) wasadded and the mixture was stirred for 6 hours at 24° C. to perform apolymerization reaction. Furthermore, this mixture was diluted with NMPto obtain 6% by weight solution of the polyimide precursor (PI-4).

The number average molecular weight (Mn) and weight average molecularweight (Mw) of the produced polyimide precursor (PI-4) were Mn=16,100and Mw=33,500, respectively.

Synthesis Example 5 Polymerization of Polyimide Precursor (PI-5)

Under nitrogen stream, 8.01 g (0.040 mol) of 4,4′-diaminodiphenylether(hereinafter, DDE) was fed into a 200 ml four-neck flask and dissolvedinto 87.6 g of NMP. Subsequently, 7.45 g (0.038 mol) of CBDA was addedand the mixture was stirred for 5 hours at 23° C. to perform apolymerization reaction. Furthermore, this mixture was diluted with NMPto obtain 6% by weight solution of the polyimide precursor (PI-5).

The number average molecular weight (Mn) and weight average molecularweight (Mw) of the produced polyimide precursor (PI-5) were Mn=14,000and Mw=32,600, respectively.

Synthesis Example 6 Polymerization of Polyimide Precursor (PI-6)

Under nitrogen stream, 8.01 g (0.040 mol) of DDE was fed into a 200 mlfour-neck flask and dissolved into 91.9 g of NMP. Subsequently, 8.20 g(0.038 mol) of PMDA was added and the mixture was stirred for 2 hours at23° C. to perform a polymerization reaction. Furthermore, this mixturewas diluted with NMP to obtain 6% by weight solution of the polyimideprecursor (PI-6).

The number average molecular weight (Mn) and weight average molecularweight (Mw) of the produced polyimide precursor (PI-6) were Mn=11,500and Mw=25,200, respectively.

Tetracarboxylic acid anhydrides and diamines, and compounds thereof usedin Synthesys Examples are shown below.

TABLE 12 Tetracarboxylic Molecular weight acid anhydride Diamine of PICBDA TDA BODA PMDA DA-25 DDE Mn Mw PI-1 ◯ ◯ 17,000 38,300 PI-2 ◯ ◯ 5,2007,900 PI-3 ◯ ◯ 4,900 7,200 PI-4 ◯ ◯ 16,100 33,500 PI-5 ◯ ◯ 14,000 32,600PI-6 ◯ ◯ 11,500 25,200

Example 1

Ultraviolet Ray Sensitivity Characteristics of Polyimide Cured FilmFormed from PI-1

The solution of PI-1 prepared in Synthesis Example 1 was dropped byusing a syringe equipped with a filter having 0.2 μm pores, and appliedto an ITO-deposited glass substrate (2.5 cm squire, thickness 0.7 mm) bythe spin coating method. Subsequently, the coating was subjected to heattreatment on a hot plate of 80° C. for 5 minutes, and the organicsolvent was evaporated. Then, the coating was baked on the hot plate of230° C. for 60 minutes to produce a polyimide film having a filmthickness of about 200 nm. The contact angle to water of this polyimidefilm was measured.

The surface of the polyimide film produced by a similar procedure wasirradiated with ultraviolet rays in irradiation amount of 20 J/cm² or 30J/cm². The contact angle to water of each irradiated film was measured.

The measurement result of the contact angle to water is shown in Table13.

Example 2

Ultraviolet Ray Sensitivity Characteristics of Polyimide Cured FilmFormed from PI-2

A polyimide film was prepared by using a similar method in Example 1using the solution of PI-2 prepared in Synthesis Example 2. The contactangles to water of the ultraviolet ray non-irradiation film and thefilms after irradiation of 20 J/cm² or 30 J/cm² were measured.

The measurement result of the contact angle to water is shown in Table13.

Example 3

Ultraviolet Ray Sensitivity Characteristics of Polyimide Cured FilmFormed from PI-3

The polyimide film was prepared by using a similar method in Example 1using the solution of PI-3 prepared in Synthesis Example 3. The contactangles to water of the ultraviolet ray non-irradiation film and thefilms after irradiation of 20 J/cm² or 30 J/cm² were measured.

The measurement result of the contact angle to water is shown in Table13.

Example 4

Ultraviolet Ray Sensitivity Characteristics of Polyimide Cured FilmFormed from PI-4

The polyimide film was prepared by using a similar method in Example 1using the solution of PI-4 prepared in Synthesis Example 4. The contactangles to water of the ultraviolet ray non-irradiation film and thefilms after irradiation of 20 J/cm² or 30 J/cm² were measured.

The measurement result of the contact angle to water is shown in Table13.

Comparative Example 1

Ultraviolet Ray Sensitivity Characteristics of Polyimide Cured FilmFormed from PI-5

The polyimide film was prepared by using a similar method in Example 1using the solution of PI-5 prepared in Synthesis Example 5. The contactangles to water of the ultraviolet ray non-irradiation film and thefilms after irradiation of 20 J/cm² or 30 J/cm² were measured.

The measurement result of the contact angle to water is shown in Table13.

Comparative Example 2

Ultraviolet Ray Sensitivity Characteristics of Polyimide Cured FilmFormed from PI-6

The polyimide film was prepared by using a similar method in Example 1using the solution of PI-6 prepared in Synthesis Example 6. The contactangles to water of the ultraviolet ray non-irradiation film and thefilms after irradiation of 20 J/cm² or 30 J/cm² were measured.

The measurement result of the contact angle to water is shown in Table13.

TABLE 13 Ultraviolet ray irradiation amount and contact angle to waterNo. Used PI Non-irradiation 20 J/cm² 30 J/cm² Example 1 PI-1 64°  6°  6°Example 2 PI-2 63° 10°  6° Example 3 PI-3 53° 16°  6° Example 4 PI-4 58°30° 30° Comparative PI-5 62° 42° 20° Example 1 Comparative PI-6 69° 65°63° Example 2

As shown in Table 13, Examples 1 to 4 corresponding to the cured filmsproduced from the polyimide precursor or the polyimide according to thepresent invention showed significant change of the contact angle towater even in low exposure amount (20 J/cm²) compared with ComparativeExamples 1 and 2 corresponding to related-art materials.

INDUSTRIAL APPLICABILITY

The polyimide precursor and the polyimide according to the presentinvention can shorten the exposure time required for alteringhydrophilicity/hydrophobicity. Therefore, it can be expected that themanufacturing cost in the patterning layer formation of a functionalmaterial, such as an electrode is reduced.

In addition, it is possible to impart anisotropy to the film producedfrom the polyimide precursor and the polyimide according to the presentinvention by polarized ultraviolet (UV) irradiation. This means that thefilm can be used as an orientation treatment film for functionalmaterials such as liquid crystals and semiconductors. Therefore, it isexpected that the manufacturing time can be shortened similarly to thecase of using the film as a base film for image formation.

1. A polyimide precursor having a structure represented by the followingformula (1):

(where A represents a tetravalent organic group; B represents a bivalentorganic group having a thiol ester bond in its main chain; R¹ and R²independently represent a hydrogen atom or a univalent organic group;and n represents a natural number).
 2. The polyimide precursor accordingto claim 1, wherein A in the formula (1) represents a tetravalentorganic group having an aliphatic ring or made of only an aliphaticgroup.
 3. The polyimide precursor according to claim 1, wherein B in theformula (1) represents a bivalent organic group represented by thefollowing formula (2):

(where X and Y independently represent an aromatic ring or an aliphaticring, and these rings are optionally substituted by a halogen atom or analkyl group having 1 to 4 carbon atom(s)).
 4. The polyimide precursoraccording to claim 1, wherein the polyimide precursor is produced bypolymerizing at least one type of tetracarboxylic acid dianhydriderepresented by the following formula (3) and a derivative thereof withat least one type of a diamine represented by the following formula (4):

(where A represents a tetravalent organic group and B represents abivalent organic group having a thiol ester bond).
 5. A polyimideproduced by dehydrating and ring closing the polyimide precursor asclaimed in claim
 1. 6. A coating solution for an under layer film forimage formation comprising: at least one type of a compound selectedfrom a group consisting of the polyimide precursor as claimed in claim 1and a polyimide produced by dehydrating and ring closing the polyimideprecursor as claimed in claim
 1. 7. A cured film produced by curing thecoating solution for an under layer film for image formation as claimedin claim
 6. 8. An under layer film for image formation produced by usingthe coating solution for an under layer film for image formation asclaimed in claim
 6. 9. An under layer film for electrode patternformation produced by using the coating solution for an under layer filmfor image formation as claimed in claim
 6. 10. A gate insulating filmproduced by using the coating solution for an under layer film for imageformation as claimed in claim
 6. 11. A method for forming an under layerfilm for image formation, comprising: applying the coating solution foran under layer film for image formation as claimed in claim 6 applied ona substrate, thermosetting it, and irradiating it with an ultravioletray.